Why does my system now have shrill top end.

Yes but this issue started in the Summer and now it is Fall so change in humidity did not have any effect.

Yes, the humidity shift happens at about 45%.

Above that it is dissipative. static will bleed off.

Below that, it will begin to build. The effect is subtle but persistent, and worsens as the dryer it becomes.

It's not just the carrier as an issue it's the static.

The next possibility is a degrading of electrical connections, with regard to impedance at the interface, due to oxidation, contact quality degradation, etc.

Next, that some critical component or aspect is right on the ragged edge of being overly revealing and overly analytical. As combinations go, that is.

Anything with outboard power supplies and an umbilical connection to said power supply is especially vulnerable to contact degradation in the connecting umbilical. Check those connections. Reinsert, tighten, etc.

Thanks for the advice. I assume the ac cables do not degrade themselves.

Have you changed anything in your room? Added a coffee table, moved speakers, etc? Have you changed where you sit? 

Aging equipment (a cap has degraded) or a loose connection.